The Amazing Slow Downer will work with downloaded MP4 videos - audio-only, of course.

thanks guys

I like " the Ultimate dvd player. Down load the you tube video. Burn it to a disc then use this program. Slows down video without changing the pitch!

I like the 'Amazing Ears'. Extract the audio from the video and use all kinds of software to slow it down.

I download a YouTube video with "Fastest YouTube Downloader". This converts the video into an MP3. I then put the MP3 file into an iTunes playlist. I open The Amazing Slowdowner and import that playlist. Now I can select a single tune and play it as slow speeds with out changing the pitch. It sounds complicated but it really isn't. I have been doing this for years and it works very well. I learned most of my Cajun songs on the Amazing Slowdowner. This will work for both Mac and Windows. Try it. You'll like it.

You see, every madman here has his own method.
But if you really want a slow VIDEO (so you can watch what the fingers are doing) I would recommend my method! Good Luck!